Multielement radio-frequency antenna structure having linear and helical conductive elements

ABSTRACT

A multi-element antenna structure is provided which may be fabricated with an improved characteristic impedance for impedance matching purposes. The elements in an antenna include both linear and helical electrically conductive elements that are structurally supported and protectively encased in a dielectric material comprising a fiber-glass-reinforced synthetic resin matrix.

United States Patent [1 1 Francis, deceased [451 Nov. 20, 1973MULTIELEMENT RADIO-FREQUENCY ANTENNA STRUCTURE HAVING LINEAR AND HELICALCONDUCTIVE ELEMENTS [76] Inventor: Richard J. Francis, deceased, late ofPataskala, Ohio by Clara A. Francis, executrix [22] Filed: June 20, 1972[21] Appl. No.: 264,624

Related [15. Application Data [63] Continuation of Ser. No. 53,062, July8, 1970,

abandoned.

[52] U5. Cl 343/749, 343/787, 343/873, 343/895, 343/897, 343/900 [51]Int. Cl. H01g 1/40, HOlg 1/36, HOlg 9/30 [58] Field of Search 343/749,873, 895, 343/897, 900, 787

[5 6] References Cited UNITED STATES PATENTS 2,681,412 6/1954 Webster343/895 X 2,748,386 5/1956 Polydoroff 343/787 6/1935 Round 343/895 X8/1963 Foley 343/895 OTHER PUBLICATIONS Freedman, G String Transmissionand Helical Wave Coils in Radio Electronics June, 1951; pp. 24-25"Takeichi-Unequal-Multiconductor Unipole Antennas in Electronics andCommunications in Japan May, 1966 TK 7800E593; pp. 45-53 PrimaryExaminer-Rudolph V. Rolineo Assistant Examiner-Marvin NussbaumAttorneyRobert E. Stebens [5 7 ABSTRACT A multi-element antennastructure is provided which may be fabricated with an improvedcharacteristic impedance for impedance matching purposes. The elementsin an antenna include both linear and helical electrically conductiveelements that are structurally supported and protectively encased in adielectric material, comprising a fiber-glass-reinforced synthetic resinmatrix.

14 Claims, 11 Drawing Figures PATENTEU 2 75 SHEET 18F 2 INVENTORS.RICHARD J. FRANCIS & Y CLARA A. FRANCIS B MAHO NEY, MILLER & STEBENSWE/WW ATTORNEYS PATENTEU Z HYS SHEET 20? 2 5 Lu N a P (I) M 2 2 O 0 l QU) 8 m D: Q:

FREQUENCY FREQUENCY INVENTORS. RICHARD J- FRANCIS & BYCLARA A. FRANCISMAHONEY MILLER STEBENS ATTORNEYS MULTIELEMENT RADIO-FREQUENCY ANTENNASTRUCTURE HAVING LINEAR AND HELICAL CONDUCTIVE ELEMENTS This applicationis a continuation of Ser. No. 53,062, filed July 8, 1970, now abandoned.

BACKGROUND OF THE INVENTION The antenna structure of this invention isprimarily adapted to mobile installations for both transmitting andreceiving functions such as citizens-band operations in connection withautomotive vehicles although the antenna structure is adaptable to otherfrequency band allocations. In installations of this type, the antennasof prior art constructions comprises a single electrically conductiveelement effective as both a receiver and radiator of electromagneticwave energy in the radio-frequency spectrum and is of a physicalconstruction to accomodate the mechanical forces that may be applied asa consequence of vehicular movement. Antennas of prior art constructionfor mobile installations are most commonly an electrical quarter wave inlength and metallic ranging in length from about 9 feet for 27 megahertzto about 6 inches for 470 megahertz. These antennas are usuallyvertically mounted and supported only at the bottom and are end-fed.Vertical quarter wave antennas of a length in the range of 9 feet arephysically unwieldly; however, an antenna in the l OO megahertz rangemay be physically shortened by adding inductance in series. Conversely,the physical length, commonly called aperture, may be increased byadding capacitance in series.

Quarter-wave antennas are desirable because, when end-fed, they approachresonance. Resonance is the state where inductance and capacitivereactances are equal, but, since they are of opposite sign, theresultant total impedance of the antenna is its resistance whichincludes both radiation resistance and loss resistance.

In twoway radio communications, the transceiver and antenna areconnected with coaxial cable, and the most commonly used coaxial cablehas a characteristic impedance of 52 ohms. The output stage of thetransceiver is adjustable to 52 ohms. However, the terminal impedance ofan end-fed quarter wave is well below 52 ohms, perhaps as low as ohms.Maximum power transmission results when the terminal impedance of theend-fed quarter wave antenna matches the impedance of the coaxialtransmission line. With the single element antennas of prior art theimpedance mis-match is great enough to seriously impede the efficiencyof power transferral. Some installations are operated inefficiently withthis mis-match, while other installations rely on complex impedancematching networks to correct this mis-match.

BRIEF DESCRIPTION OF THE INVENTION The antenna structure provided bythis invention comprises a multiplicity of elements including bothlinear elements and helical elements that are electricallyinterconnected to form a composite structure having the desiredimpedance at the design operating frequency of a particular antennastructure. This multiple element design enables construction of anantenna having a more advantageous impedance match with that of aconnecting coaxial transmission cable. A desired nominal operatingfrequency within a frequency band throughout the 1 --S00 megahertzspectrum is readily obtained for a particular antenna structure throughappropriate selection of the component elements and physicalconfiguration of each element while providing prises as the electricallyconductive elements thereof,

a combination of linear elements and helical elements with there being aplurality of either the linear elements or the helical elements. Otherembodiments may comprise pluralities of both linear elements and helicalelements in various combinations. A structurally supporting body isformed for the selected elements from a dielectric material such as asynthetic resin reinforced with strands of fiber glass with thecompleted structure capable of accomodating the structural or mechanicalforces encountered in a mobile vehicular installation. These and otherobjects and advantages of this inven tion will be readily apparent fromthe following detailed description of embodiments thereof and theaccompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary elevational viewpartly in section, of an antenna structure embodying this invention.

FIG. 2 is a transverse sectional view taken along line 2-2 of FIG. 1.

FIG. 3 is a transverse sectional view taken along line 3-3 of FIG. 1.

FIG. 4 is a diagrammatic illustration of the electrical equivalentcircuit of the antenna structure of FIG. 1.

FIGS. 5 and 6 are graphic representations of the frequency responsecharacteristics of the elements forming the antenna structure.

FIGS. 7-11 are diagrammatic illustrations of the electrical equivalentcircuits of modified antenna structures embodying this invention.

DETAILED DESCRIPTION OF THE INVENTION Having reference to FIGS. 1-3 ofthe drawings, an antenna structure embodying this invention isillustrated in detail. This antenna structure comprises a multiplicityof electrically conductive elements, indicated generally at 10, encasedin a structurally supporting body 11 that includes a central core 12 andan outer coaxially formed sheath 13 although the core 12 and sheath 13are preferably integrally formed in fabrication of a composite antenna.In this embodiment, the four elements 15, l6, l7 and 18 are arranged inpairs thus forming two members which are effective, at the design radiofrequencies, for radiation or reception of electromagnetic wave energyor two elements 15 and 16 are helically coiled to define an elongatedcylinder and are each serially connected with a respective linearelement 17 and 18.

The conductive elements 15, 16, 17 and 18 are preferably formed fromsmall diameter copper wire, such as No. 24 A. W. G., to obtain thedesired electrical characteristics and, consequently, the elements willnot be structurally self-supporting. An antenna structure of thisinvention is particularly adapted to utilization with mobile vehicularinstallations and these installations are normally operated in the l 500megahertz frequency spectrum where a quater-wave antenna will have asubstantial length. In the case of equipment operating in thecitizens-band frequency spectrum at the nominal operating frequency ofI27 megahertz, the physical length for an electrical quarter-wave lengthwill be of the order of 3 to 8 feet and it will be readily seen thatthis length precludes reliance on the structural strength of theconductive elements for structural integrity of the antenna structure.Accordingly, a structurally supporting body 11 is provided to adequatelymaintain the several conductive elements in a specific configuration andpermit vertical mounting of the antenna on a vehicle. This body 11 isformed from a dielectric material which is a synthetic resin matrixhaving the necessary mechanical characteristics as to flexural strengthand modulus for the specific design application to withstand the staticand dynamic loads that may be encountered in vehicular installations andmaintain the specific element configuration. Preferably, the syntheticresin matrix which may comprise a thermosetting polyester or epoxy, alsoincludes strands of fiber glass 19 distributed throughout the body toenhance the mechanical properties of the antenna structure. Thesestrands of fiber glass 19 are preferably oriented longitudinally of theantenna structure and are included in both the core 12 about which thehelical elements 15 and 16 are wound and the outer sheath 13.

Interconnection of the antenna with radio installation, as well asmechanical support or mounting of the antenna, is accomplished by meansof a mounting ferrule 20. The ferrule 20 is formed from an electricallyconductive metal with a central socket 21 in which an end of the antennastructure is inserted and secured as by a suitable adhesive or bondingmaterial. The terminal ends of the conductive elements 15 and 16 extendinto an aperture 22 formed in the ferrule and are electrically connectedto the ferrule as by a solder connection 23. The ferrule 20 is alsoprovided with a threaded portion 24! for mechanical interengagement witha mounting socket (not shown).

The two helical elements 15 and 16 may be formed conveniently bysimultaneously winding both elements on the core 12 which is performedin a preliminary step in the antenna fabrication process. Each turn ofthe helix is longitudinally spaced from an adjacent turn, a distance ofthe order or l/l6 inch in the 27 megahertz embodiment with the corediameter or internal diameter of the helical elements being of the orderof 54-: inch. The diameter of the outer sheath 13 may be of the order ofas inch and will become integral with the core 12 during thethermosetting step thereby providing a unitary structure. At least oneof the helical elements, 15 or 16, may be provided with a dielectricsheath 25 to assure electrical insulation of the two elements throughouttheir length except for the terminal ends electrically interconnected bythe solder 23. This dielectric sheath 25 in the present embodimentcomprises a suitable varnish; however, other well-known materials thatdo not provide electromagnetic shielding may be utilized. If desired,the dielectric sheath 25 may be omitted if the element spacing isotherwise maintained or both elements may be provided with a similardielectric sheath.

Connected to each helical element 15, 16 at the end opposite the solderconnection 23 is a respective one of the two linear elements 17, 18which extend longitudinally in axial alignment to the helical elements.The linear elements 17, 18 are also electrically insulated from eachother as by a dielectric sheath 26 which may also be varnish applied toone of the elements. These linear elements 17, 18 are disposed in spacedparallel relationship but are not electrically connected at their freeends thus preventing electric current circulation within the pairs ofconductive elements 15, 17 and 16, 18.

Through selection of conductive elements 15, 16, 17 and 18 ofappropriate cross-sectional area and length and through proper spacingof the elements, an antenna structure may be constructed having apredetermined value of antenna input impedance. In the usual mobileinstallation, the desired antenna input impedance for proper matching is52 Q as this is the impedance of the most commonly usedcommercially'available coaxial transmission cable.

The antenna structure of this invention will preferably be aquarter-wave length for the specific design frequency band. One of theparameters controlling the physical length of an end-fed electricalquarter-wave antenna is the diameter of the conductor. For a givenelectrical quarter-wave, the physical length of the conductor decreasesas the conductor diameter increases, but not as a straight linefunction. FIG. 5 illustrates this condition. Curve M shows the responseof a conductor of a given diameter, while curve N is the response of aconductor of another diameter. FIG. 5 shows that their resonantfrequencies are at different frequency values in the spectrum andillustrates how a multiplicity of conductors of dissimilar diametersbroadens the effective band-width of an antenna.

FIG. 6 illustrates how conductors of different physical lengths havetheir maximum response at dissimilar frequencies when end-fed asquarter-wave antennas. Curves P and S represent conductors of differentphysical lengths, and their resonant frequencies may be widelydisplaced.

A slight difference in length of the pairs of conductive elements 15, 17and 16, 18 is obtained in the illustrated embodiment where the twohelical elements 15 and 16 are seen to be of dissimilar diameters. Thisresults from the two elements being wound with the same pitch with thesame internal diameter and this causes the pitch diameter whichdetermines the lineal dimension to be different. The larger diameterelement of 15 and 16 will thus be longer. A further change in length canbe obtained through adjustment in relative length of the two linearelements 17 and 18.

Utilizing a combination of helical and linear elements permitsfabrication of an antenna having improved impedance match throughappropriate relative dimensioning of the helical and linear elements andalsohaving a better resonance characteristic.

The central core 12 may also comprise a ferrite material having amagnetic permeability greater than unity to further enhance theelectrical properties of the antenna structure. Ferrites such as ironcarbonyls and magnetic iron oxide in particulate form may be embedded inand distributed throughout the resin matrix forming the core 12.

Other antenna structures embodying this invention may be constructedwith various combinations of helical and linear elements. Severalcombinations are diagrammatically illustrated in FIGS. 7-11 which may bereadily fabricated utilizing the previously set forth detailedconstruction principles relative to the form shown in FIG. 4 to obtainspecific antenna characteristics. FIG. 7 illustrates a configurationopposite or inverted to that previously described with the linearelements being electrically interconnected and forming the end fedterminal connection. The configurations shown in H68. 3 and 9 arefurther variations of the embodiment described in detail in that thelinear or helical elements may be formed in separate sections having theother elements interposed at an intermediate point. FIGS. ill and illillustrate embodiments that include either a single helical element orsingle linear element while having a plurality of the other elements. Inthese embodiments, the single element is connected to an antennaterminal connection with the multiple elements being electricallyinterconnected at one end and to the single element. It will be apparentthat combinations other than those illustrated may be fabricated such ashaving more than two conductive pairs or having multiples of theconfigurations shown in FIGS. 10 and ll.

It will be readily apparent that a novel antenna structure is providedwhich may be readily constructed with the desired impedance at theconnector terminal for optimum matching with the impedance of aninterconnecting cable. Utilizing conductive elements of dissimilardiameters and lengths widens the frequency response and a desiredantenna characteristic is obtained through appropriate combination oflinear and helical elements.

I claim:

1. A radio-frequency antenna structure comprising a linear elementformed from an elongated, longitudinally extending electrical conductorand a plurality of helical elements axially disposed relative to saidlinear element, said helical elements being elongated electricalconductors formed into cylindrical helixes of the same pitch andinternal diameter disposed in coaxial, side-by-side relationship witheach element electrically insulated from the other throughout theirlength but all being electrically connected together at one end, saidlinear element series connected electrically at one end with saidhelical elements at their interconnected ends with the other end of saidlinear element forming a connecting terminal of the antenna, saidhelical and linear element conductors being of selected cross-sectionalarea to provide a desired antenna impedance, and a body structure formedfrom a dielectric material in which said linear and helical elements areembedded for support thereof in relatively fixed relationship saiddielectric material having a relatively low loss characteristic as toelectromagnetic wave energy and physical strength characteristic tomaintain the physical configuration of the conductive elements andassure structural integrity of the antenna structure.

2. An r-f antenna structure according to claim 1 wherein said dielectricmaterial is a snythetic resin matrix reinforced with strands of fiberglass extending longitudinally throughout the length of the antennastructure.

3. An r-f antenna structure according to claim I having a central corearound which said helical elements are wound with said core formed froma material having a magnetic permeability greater than unity.

d. An r-f antenna structure according to claim ll wherein said helicalelements are of dissimilar crosssectional area to provide a relativelygreater effective band width at the nominal operating frequency.

5. An r-f antenna structure according to claim ll wherein said helicalelements are of dissimilar lengths to provide a relatively greatereffective bandwidth at the nominal operating frequency.

6. A radio-frequency antenna structure comprising a plurality of linearelements of elongated, longitudinally extending electrical conductorsdisposed in spaced parallel relationship electrically insulated one fromanother throughout their length, a plurality of helical elements ofelongated electrical conductors formed into cylindrical helixes of thesame pitch and internal diameter disposed in coaxial, side-by-siderelationship electrically insulated one from another throughout theirlength, said linear and helical elements relatively axially disposedwith each of said linear elements series connected electrically with arespective one of said he lical elements and having all of the seriesconnected elements electrically interconnected at an end point formingan antenna terminal, said linear and helical element conductors being ofselected cross-sectional area to provide a desired antenna impedance,and a body structure formed from a dielectric material in which saidlinear and helical elements are embedded for support thereof inrelatively fixed relationship, said dielectric material having arelatively low loss characteristic as to electromagnetic wave energy andphysical strength characteristic to maintain the physical configurationof the conductive elements and assure structural integrity of theantenna structure.

7. An r-f antenna structure according to claim 6 wherein said dielectricmaterial is synthetic resin matrix reinforced with strands of fiberglass extending longitudinally throughout the length of the antennastructure.

d. An r-f antenna structure according to claim 6 having a central corearound which said helical elements are wound with said core formed froma material having a magnetic permeability greater than unity.

9. An r-f antenna structure according to claim 6 wherein said linearelements are electrically interconnected together at one end to formsaid antenna terminal.

10. An r-f antenna structure according to claim 9 having a helicalelement intermedially interposed in each linear element.

ill. An r-f antenna structure according to claim 6 wherein said helicalelements are electrically interconnected together at one end to form.said antenna terminal.

112. An r-f antenna structure according to claim 11 having a linearelement intermedially interposed in each helical element.

13. An r-f antenna structure according to claim 6 wherein said linearand helical elements are of dissimilar cross-sectional area to provide arelatively greater effective band width at the nominal operatingfrequency.

114. An r-f antenna structure according to claim 6 wherein said seriesconnected linear and helical elements are of dissimilar lengths toprovide a relatively greater effective band width at the nominaloperating frequency.

UNITED STATES PATENT OFFICE, CERTIFICATE OF CORRECTION Patent No. 3 774221 Dated November 20 1973 Inventofl Richard J. Francis and Clara A.Francis It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

On the title page;

at item [19] after "Francis, deceased", insert --et al.

at item [76'] after "executrix", insert, --and Clara A. Francis, 11855Broad Street, Pataskala Ohio 43062--.

Signed and sealed this 2nd day of April 197A.

(SEAL) Attest: v

EDWARD M.FLETCHER,JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PO-105O (10-69) USCOMNPDC xi-[sung u.s. GOVERNMENT PRINTINGOFFICE: an 0-

1. A radio-frequency antenna structure comprising a linear elementformed from an elongated, longitudinally extending electrical conductorand a plurality of helical elements axially disposed relative to saidlinear element, said helical elements being elongated electricalconductors formed into cylindrical helixes of the same pitch andinternal diameter disposed in coaxial, side-by-side relationship witheach element electrically insulated from the other throughout theirlength but all being electrically connected together at one end, saidlinear element series connected electrically at one end with saidhelical elements at their interconnected ends with the other end of saidlinear element forming a connecting terminal of the antenna, saidhelical and linear element conductors being of selected crosssectionalarea to provide a desired antenna impedance, and a body structure formedfrom a dielectric material in which said linear and helical elements areembedded for support thereof in relatively fixed relationship saiddielectric material having a relatively low loss characteristic as toelectromagnetic wave energy and physical strength characteristic tomaintain the physical configuration of the conductive elements andassure structural integrity of the antenna structure.
 2. An r-f antennastructure according to claim 1 wherein said dielectric material is asnythetic resin matrix reinforced with strands of fiber glass extendinglongitudinally throughout the length of the antenna structure.
 3. An r-fantenna structure according to claim 1 having a central core aroundwhich said helical elements are wound with said core formed from amaterial having a magnetic permeability greater than unity.
 4. An r-fantenna structure according to claim 1 wherein said helical elements areof dissimilar cross-sectional area to provide a relatively greatereffective band width at the nominal operating frequency.
 5. An r-fantenna structure according to claim 1 wherein said helical elements areof dissimilar lengths to provide a relatively greater effectivebandwidth at the nominal operating frequency.
 6. A radio-frequencyantenna structure comprising a plurality of linear elements ofelongated, longitudinally extending electrical conductors disposed inspaced parallel relationship electrically insulated one from anotherthroughout their length, a plurality of helical elements of elongatedelectrical conductors formed into cylindrical helixes of the same pitchand internal diameter disposed in coaxial, side-by-side relationshipelectrically insulated one from another throughout their length, saidlinear and helical elements relatively axially disposed with each ofsaid linear elements series connected electrically with a respective oneof said helical elements and having all of the series connected elementselectrically interconnected at an end point forming an antenna terminal,said linear and helical element conductors being of selectedcross-sectional area to provide a desired antenna impedance, and a bodystructure formed from a dielectric material in which said linear andhelical elements are embedded for support thereof in relatively fixedrelationship, said dielectric material having a relatively low losscharacteristic as to electromagnetic wave energy and physical strengthcharacteristic to maintain the physical configuration of the conductiveelements and assure structural integrity of the antenna structure.
 7. Anr-f antenna structure according to claim 6 wherein said dielectricmaterial is synthetic resin matrix reinforced with strands of fiberglass extending longitudinally throughout the length of the antennastructure.
 8. An r-f antenna structure according to claim 6 having acentral core around which said helical elements are wouNd with said coreformed from a material having a magnetic permeability greater thanunity.
 9. An r-f antenna structure according to claim 6 wherein saidlinear elements are electrically interconnected together at one end toform said antenna terminal.
 10. An r-f antenna structure according toclaim 9 having a helical element intermedially interposed in each linearelement.
 11. An r-f antenna structure according to claim 6 wherein saidhelical elements are electrically interconnected together at one end toform said antenna terminal.
 12. An r-f antenna structure according toclaim 11 having a linear element intermedially interposed in eachhelical element.
 13. An r-f antenna structure according to claim 6wherein said linear and helical elements are of dissimilarcross-sectional area to provide a relatively greater effective bandwidth at the nominal operating frequency.
 14. An r-f antenna structureaccording to claim 6 wherein said series connected linear and helicalelements are of dissimilar lengths to provide a relatively greatereffective band width at the nominal operating frequency.